Added a braindead implementation of ListingProxy.List.
Added a braindead implementation of ListingProxy.List.

jacobsa/timeutil,GoogleCloudPlatform/gcsfuse,jacobsa/ratelimit,kahing/gcsfuse,BanzaiMan/gcsfuse,mbrukman/gcsfuse,GoogleCloudPlatform/gcsfuse,GoogleCloudPlatform/gcsfuse,BanzaiMan/gcsfuse